The invention relates to a cutting guide for bone preparation and more particularly to a cutting guide for preparing a bone for receipt of a stem of a prosthesis wherein the cutting guide is adjustable to facilitate cutting the bone in a plane that is adjustable anteriorly and posteriorly, laterally and medially, and in any combination thereof.
During shoulder arthroplasty, the humeral head must be resected to allow for the insertion of a humeral stem into the intramedullary canal of the humerus. The proximal end of the humerus includes the humeral head which articulates with the glenoid cavity of the shoulder in a ball and socket fashion. The humeral head is nearly hemispherical in form.
The prostheses typically used for shoulder arthroplasty include a stem portion designed to extend into the intramedullary canal of the humerus and a head portion designed to replace the humeral head. The head portion of the prosthesis extends angularly from the stem portion. The resection of the natural humeral head must be made so that the angle of the cut corresponds to the angle between the stem and head portions of the prosthesis. In addition, the rotation of the cut varies to adjust to bone wear or capsulor looseness.
There are eight essential variables relating to humeral arthroplasty. These include: the diameter of curvature of the prosthesis; the percentage of the sphere with this diameter that will be used as prosthetic articular surface; the superior/inferior position of the articular surface relative to the humerus; the anterior/posterior position of the articular surface relative to the humerus; the medial/lateral articular aspect of the articular surface with respect to the humerus; the anterior/posterior angulation (flexion/extension) of the articular surface relative to the prosthesis; the medial/lateral angulation (varus/valgus) of the prosthesis relative to the humerus; and, the rotational alignment of the prosthetic head with respect to the humeral axis. The goal of prosthetic arthroplasty is to duplicate the normal orientation of the humeral articular surface as well as its diameter of curvature and percentage of the sphere.
Many orthopaedic companies currently provide anatomically variable prosthesis with stems that facilitate adjusting the prosthesis to more accurately reflect the anatomy of the individual. For anatomically variable prostheses, most surgical techniques call for a “freehand” cut of the humeral head. Others have rudimentary guides that facilitate a planar cut but only allow for anterior/posterior (version) or medial/lateral adjustment of the cutting plane.
When the humeral head resection is made free hand, the elbow of the patient is flexed to 90° with the patient's forearm aimed at the midline of the operating surgeon's trunk. The humerus is externally rotated to provide the recommended degree of retrotorsion in relation to the axis of elbow motion. The resection is directed away from the surgeon, allowing the surgeon to reproduce the desired retrotorsion in the bone cut. A trial prosthesis may also be placed along the proximal humeral shaft as a guide for the proper inclination of the resection. The possibility for error exists with this free hand approach. Inaccurate resection can result in an ill-fitting prosthesis which may cause complications for the patient and may eventually require replacement of the prosthetic device.
Even when a cutting guide is utilized by the surgeon to ensure that the humeral head is resected along a plane of resection, the cutting guide places limits on the orientation of the plane of resection. The plane of resection includes both an anterior/posterior angle and a medial/lateral angle. Current humeral cutting guide designs only allow for the removal of the humeral head to be made at a selectable anterior/posterior angle or a set medial/lateral angle. Thus, the medial/lateral angle of the cutting plane cannot be adjusted in concert with the anterior/posterior angle with such cutting guides. Accordingly, the cut cannot be made along every potentially desired plane in three-dimensional space. Thus the surgeon has limited ability to make a cut that best matches the anatomy of each individual.
Many humeral cutting guides are adapted to clamp onto a reamer used to ream into the intramedullary canal prior to resection of the humeral head to provide a cavity into which a stem of a humeral prosthesis will be inserted. Following the reaming operation, the reamer is used as a temporary anchor for the cutting guide prior to adjustment of the angle of the cutting guide.
Accordingly, the need exists for a humeral cutting guide which will ensure an exact and precise resection of the humeral head. It would be desirable to have a cutting guide that allows for infinite variability of the cutting plane.
The disclosed humeral cutting guide allows for anterior/posterior and medial/lateral adjustment of the cutting plane to correspond to a humeral stem. The disclosed cutting guide is not only adjustable in the anterior/posterior direction, but also allows for the cut to be made in any direction in three-dimensional space. This gives the surgeon the opportunity to make a cut that can better match the anatomy of each individual.
The disclosed humeral cutting guide allows for the resection of the humeral head in any orientation in three-dimensional space. The guide locks on the reamer in a standard fashion. Additionally, the guide surface can be locked in an easily found zero position corresponding to a typical humeral head configuration.
According to one aspect of the disclosure, an adjustable humeral cutting guide for defining a cutting plane for a saw in a bone using a positioning structure is provided. The cutting guide includes a clamp, a saw guide, and an orientable coupling. The clamp is configured to be secured to the positioning structure. The saw guide includes a slot formed therein sized to receive a saw and limit the saw to cutting in a specific plane. The orientable coupling is mounted to the clamp and the saw guide. The orientable coupling is configured to adjust the saw guide at a selectable anterior/posterior angle and a selectable medial/lateral angle.
According to another aspect of the disclosure, an adjustable cutting guide for resection of a bone comprises a positioning structure, a clamp, a member, a saw guide and an orientable coupling. The positioning structure is configured to be at least temporarily fixed relative to the bone. The clamp is adapted to be coupled to the positioning structure for movement longitudinally with respect to a longitudinal axis of the bone and radially about the longitudinal axis of the bone. The member is coupled to the clamp for movement relative to the clamp in a direction transverse to the longitudinal axis of the bone. The saw guide defines a resection plane of reference for a saw received therein. The orientable coupling extends between the saw guide and member and facilitates adjustment of the resection plane of reference in three dimensions.
According to yet another aspect of the disclosure, an apparatus for guiding the resection of the head of a humerus comprises an intramedullary alignment member, an extramedullary alignment member, a translatable member, a saw guide and an orientable coupling. The intramedullary alignment member has a longitudinal axis and is structured for substantial axial alignment with the intramedullary canal of a humerus. The extramedullary alignment member extends substantially perpendicularly from the intramedullary alignment member and is translatable along, and rotatable about, the longitudinal axis of the intramedullary alignment member. The translatable member is translatable along the extramedullary alignment member. The orientable coupling extends between the saw guide and the translatable member and is configured to translate with respect to the translatable member in a direction transverse to the extramedullary alignment member. The orientable coupling is also configured to orient the saw guide in an orientation relative to the head of the humerus within a range desirable for humeral resection.
The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention.